The present disclosure relates generally to the field of scanning antennas or beam-steering antennas, of the type employed in such applications as radar and communications. More specifically, this disclosure relates to a scanning or beam-steering antennas in which electromagnetic radiation is evanescently coupled between a dielectric transmission line and an antenna element having a coupling geometry, and which steer electromagnetic radiation in directions determined by the coupling geometry.
Scanning or beam-steering antennas, particularly dielectric waveguide antennas, are used to send and receive steerable millimeter wave electromagnetic beams in various types of communication applications and in radar devices, such as collision avoidance radars. In such antennas, an antenna element includes an evanescent coupling portion having a selectively variable coupling geometry. A transmission line, such as a dielectric waveguide, is disposed closely adjacent to the coupling portion so as to permit evanescent coupling of an electromagnetic signal between the transmission line and the antenna elements, whereby electromagnetic radiation is transmitted or received by the antenna. The shape and direction of the transmitted or received beam are determined by the coupling geometry of the coupling portion. By controllably varying the coupling geometry, the shape and direction of the transmitted/received beam may be correspondingly varied.
The coupling portion may be a portion of the antenna element formed as controllably variable diffraction grating, or it may be a coupling edge of the antenna element having an electrically or electromechanically variable coupling geometry. A controllably variable diffraction grating that provides a beam-steering or scanning function may be provided, for example, on the surface of a rotating cylinder or drum as disclosed in such exemplary documents as U.S. Pat. Nos. 5,571,228; 6,211,836; and 6,750,827, the disclosures of which are expressly incorporated herein by reference. An example of an antenna element having a coupling edge with a controllably variable geometry is disclosed in U.S. Pat. No. 7,151,499, the entire disclosure of which is expressly incorporated herein by reference. In this last-mentioned document, the geometry of the coupling edge is determined by a pattern of electrical connections that is selected for the edge features of the coupling edge. This pattern of electrical connections may be controllably selected and varied by an array switches that selectively connect the edge features. Any of several types of switches integrated into the structure of the antenna element may be used for this purpose, such as, for example, semiconductor plasma switches. A specific example of an evanescent coupling antenna in which the geometry of the coupling edge is controllably varied by semiconductor plasma switches is disclosed and claimed in the commonly-assigned, co-pending application Ser. No. 11/939,385; filed Nov. 13, 2007, the disclosure of which is incorporated herein by reference in its entirety.
While the prior art, as exemplified by the above-mentioned documents, provides acceptable performance in terms of beam-shaping, beam-steering and scanning, improvements are still sought in the functionality of scanning antennas. In particular, improvements in scanning accuracy and controllability in a single selected plane (e.g., the horizontal plane, or azimuth) would be an advantageous advancement in the state of the art.